This invention relates to a novel ceramics bonded product having great bonded strength and suffering hardly from cracks or breaking in the vicinity of the bonded interface even when receiving heat shock, and also to a method of producing the same.
Heretofore, as the method for bonding a metal member to a ceramics sintered body such as of alumina, there has been generally employed a method in which molybdenum paste is baked onto the surface of a ceramics sintered body, metallizing treatment is applied thereon and thereafter nickel plating is conducted, followed by soldering to effect bonding. However, this method involves a drawback that the pre-treatment procedures are very complicated.
In recent years, as substitute for such a method, studies have been made about a simpler method to bond a metal member directly to a ceramics sintered body. For example, there has been developed a method in which a metal member is brought into contact with a metal member and heated in a gas atmosphere containing a binding agent such as oxygen, or a method in which a metal member containing a binding agent is brought into contact with a ceramics sintered body and heated in a non-oxidative atmosphere.
However, according to such ceramics-metal bonded products of the prior art, the pre-treatment steps are complicated in all the methods. Besides, as compared with the coefficient of linear expansion of a ceramics sintered body, for example, that of Si.sub.3 N.sub.4 which is as small as 2.46 to 4.1.times.10.sup.-6 /.degree.C., that of conventionally employed iron is very great as 10 to 15.times.10.sup.31 6 /.degree.C., and therefore difficulties were involved in that cracks may be formed in the vicinity of the bonded interface of ceramics, even resulting in breaking in some cases.
On the other hand, as the method for bonding a ceramics sintered body to a ceramics sintered body, other than the metallizing treatment as described above, development has been made about direct bonding between a ceramics sintered body and a ceramics sintered body through a copper foil or a metal foil of the group IVa transition metal (disclosed in U.S. Pat. No. 2,857,633). However, according to the bonding method using copper foil, the bonding strength is insufficiently not higher than 10 kg/mm.sup.2, and according to any method, when abrupt heat shock is given, cracks are liable to be formed in the vicinity of the bonded surface, until it may be broken disadvantageously.